The New York Times Co. said it will launch a long-planned digital paywall this month to boost revenue at its flagship newspaper, as the media company seeks to reverse the effect of industry-wide declines that have pulled down its top line.

The Times Co. said it will launch the digital-subscription system for NYTimes.com and its mobile apps March 28. It will roll out the pay wall in its Canadian market Thursday “to fine-tune the customer experience” ahead of the worldwide release.

Shares rose 4.1 percent to $9.22 in recent trading. The stock has fallen 19 percent in the past year.

The basic plan, which includes access to both the website and smartphone app, will start at $15 every four weeks, the company said.

Readers directed to Times articles through search engines, blogs and social media links will be able to access the individual articles, even if they have reached their reading limit, though some search engines will have a daily limit of free links to Times articles.

Non-subscribers will be able to read up to 20 articles a month for free.

The erosion of company’s print advertising revenue — its largest top-line contributor — has persisted for years but has moderated since late last year, when the company suffered a 7.2% drop for its fourth quarter.